Approximate compaction and padded sorting on exclusive write PRAMs
Miroslaw Kutylowski, Tomasz Wierzbicki
Padded-sorting is a task of placing input items in an array in a
nondecreasing order, but with free space between consecutive elements
allowed. For many applications, padded-sorting is as useful as sorting.
Approximate compaction and compression are closely related problems. It
is known that time complexity of padded-sorting on randomized CRCW PRAMs
is considerably lower than time complexity of sorting. We analyze time
complexity of these problems on CREW and EREW PRAMs (deterministic and
randomized) and get tight lower und upper bounds depending on the size
of free space. We extend our lower bounds to approximate compaction and
compression.
Some of the algorithms presented are very rare examples of randomized
EREW PRAMs that are much faster than their deterministic counterparts.